1. Field of the Invention
The present invention relates to a vibratory gyroscope, and particularly, to a vibratory gyroscope which is used, for example, in a system for protecting an unsteady hold mounted on a VTR camera or the like.
2. Description of the Prior Art
FIG. 11 is a perspective view showing an example of a conventional vibratory gyroscope, FIG. 12 is a sectional view taken along the line XII--XII of FIG. 11, and FIG. 13 is a sectional view taken along the line XIII--XIII of FIG. 11. As specifically shown in FIGS. 12 and 13, the vibratory gyroscope 1 comprises a vibrator 2. The vibrator 2 comprises a regular triangular prism-shaped vibrating body 3. On centers of three side faces of the vibrating body 3, piezoelectric elements 4a, 4b and 4c are formed respectively. The vibrating body 3 is supported above a base plate 6 of 6.7 mm.times.20.4 mm in a plan view by two supporting members 5a and 5b. Furthermore, a box type case 7 of 6.7 mm width, 20.4 mm length and 5 mm height in inner sizes is fixed to the base plate 6 so as to cover the vibrating body 3 and so on. The case 7 is to protect the vibrating body 3 and so on from an outside effect.
In the vibratory gyroscope 1, upper two piezoelectric elements 4a and 4b are used for driving and detecting, lower one piezoelectric element 4c is used for feedback. When an output from the feedback piezoelectric element 4c is supplied to the driving and detecting piezoelectric elements 4a and 4b, the vibrating body 3 bends and vibrates vertically at about 25.5 kHz. In this case, the vibrating body 3 bends and vibrates forming its longitudinal center portion into an antinodal point, and two portions supported by the supporting members 5a and 5b into nodal points.
In this state, when the vibratory gyroscope 1 is rotated about the axis of the vibrating body 3 as a rotation axis, the vibrating direction of the vibrating body 3 is changed by a Coriolis force to a direction which is orthogonal to the axial direction of the vibrating body 3 but not a vertical direction. Thus, an output difference responsive to the rotational angular velocity is produced between the two driving and detecting piezoelectric elements 4a and 4b. The rotational angular velocity is detected by the output difference.
However, in the vibratory gyroscope 1 shown in FIGS. 11-13, a half-wave length of a sound wave of a vibrating frequency of the vibrating body 3 is almost equal to the inner size 6.7 mm in the width of the case 7, depending upon an environmental temperature on some occasions. That is, at an environmental temperature of about 20.degree. C. the sound velocity is about 430 m/sec., thus the half-wave length of the sound wave of about 25.5 kHz of the vibrating frequency of the vibrating body 3 becomes about 6.7 mm. In this case, at rotation of the vibratory gyroscope 1, the vibrating body 3 resonates with the case 7 to produce a standing wave, thereby its sensitivity rapidly changes. In this way, when the sensitivity of the vibratory gyroscope 1 rapidly changes, it becomes difficult to accurately detect the rotational angular velocity.